Method for determining mass flows into the inlet manifold of an internal combustion engine

ABSTRACT

A method detects mass flows to the intake manifold of an internal combustion engine having a device for controlling the air supply to the intake manifold and having a sensor for detecting the intake manifold pressure and having a control apparatus for evaluating a trace of the intake manifold pressure. In the context of the method, when the internal combustion engine is switched off, the supply of air to the intake manifold is reduced in a predetermined manner and the trace of the intake manifold pressure, which adjusts thereupon, is evaluated for detecting the mass flows.

BACKGROUND OF THE INVENTION

Examples of systems which conduct masses to the intake manifold are thetank venting and the exhaust-gas recirculation. Known methods fordiagnosing these systems are based on a detection of the mass flows tothe intake manifold. U.S. Pat. No. 4,794,790 describe, for example, adiagnostic method for a tank-venting valve wherein an idle actuator isclosed simultaneously with the opening of the tank-venting valve. In agood condition, the additional mass flow from the tank-venting system isintended to compensate for the reduction of the mass flow via the idleactuator.

For diagnosing the exhaust-gas recirculation, it is further known tomeasure the temperature increase in the intake manifold via theexhaust-gas mass flow to the intake manifold for an active exhaust-gasrecirculation.

SUMMARY OF THE INVENTION

The object of the invention is the further improvement of the selfdiagnosis of engine control systems via a detection of mass flows to theintake manifold.

In the following, the detection of mass flows in accordance with theinvention to the intake manifold of an internal combustion engine takesplace with the following:

-   -   means for controlling the air supply to the intake manifold;    -   means for detecting the intake manifold pressure; and,    -   means for evaluating the intake manifold pressure trace.

When switching off the internal combustion engine, the air supply to theintake manifold is reduced in a targeted manner and the trace of theintake manifold pressure, which results as a consequence thereof, isevaluated for making a judgment.

For example, a targeted closing of the throttle flap takes place whenswitching off the engine and an evaluation takes place of the resultingpressure trace in the intake manifold.

Stated otherwise, in accordance with the example, the reduction of theair supply takes place via a targeted closure of the throttle flap. flapis closed in a targeted manner to a defined opening angle.

A further embodiment is characterized in that no further system, whichsupplies to the intake manifold, is activated when the engine isswitched off and when there is a targeted closure of the throttle flap.

According to a further embodiment, a conclusion is drawn as to a leakagewhen the speed of a pressure change exceeds a predetermined thresholdvalue.

A further embodiment of the invention provides that a system, whichsupplies mass to the intake manifold, is actuated in a targeted mannerand a conclusion is drawn as to the mass flow of this system from acomparison of the expected intake manifold pressure trace to themeasured intake manifold pressure trace.

The invention is also directed to a control arrangement for carrying outat least one of the above methods and embodiments.

According to a further embodiment of the invention, the system, whichsupplies mass to the intake system, includes one of the followingsystems:

-   -   the exhaust-gas recirculation;    -   the tank venting; and,    -   the throttle flap at small throttle flap angles.

If the motor is shut off and the throttle flap is adjusted to a verysmall angle in a targeted manner and no additional system, whichsupplies the intake manifold, is activated, then, in each case, arelatively slow pressure increase to the ambient pressure results whenno further mass flows flow through the intake manifold except via thethrottle flap.

A leakage of the system can be concluded from a higher speed of pressurechange.

If required, a system, which supplies mass to the intake manifold (forexample, the exhaust-gas recirculation system), can be actuated in atargeted manner. A conclusion can be drawn as to the mass flow of thissystem from the comparison of the expected intake manifold pressuretrace to the measured intake manifold pressure trace.

The invention is also directed to a control apparatus for carrying outthe method as well as to further disclosed configurations.

The invention permits a throughflow diagnosis of systems which supplymass to the intake system, for example: the exhaust-gas recirculation;the tank venting; and, the throttle flap at small throttle flap anglesand a detection of leakage air inflows to the intake manifold. Inexperiments, a clear measuring effect was, for example, determined for adiagnosis of the exhaust-gas recirculation system.

It is a special advantage that mass flows can be determined withrelatively simple functions. The invention supplies an on-boarddiagnostic possibility in the context of an already-available systemcontent without additional system complexity (for example, withoutspecial additional sensors).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference the drawings wherein:

FIG. 1 shows the technical background of the invention;

FIG. 2 shows graphs illustrating the intake manifold pressure as afunction of time for explaining the invention; and,

FIG. 3 is a flowchart showing an embodiment of the method of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, 1 identifies an internal combustion engine, 2 an exhaust-gaspipe, 3 an intake manifold, 4 an intake manifold pressure sensor, 5 anelectrically adjustable throttle flap, 6 a tank-venting valve, 7 anactive charcoal filter, 8 a fuel tank, 9 an exhaust-gas recirculationvalve, 10 an accelerator pedal module and 11 a control apparatus.Numeral 12 identifies a means for displaying and/or storing diagnosticresults, for example, a fault lamp or a memory cell for storing adetailed fault code.

An air mass flows to the intake manifold flows via an open throttleflap. Further inflows are possible via the tank-venting valve 6 and/orthe exhaust-gas recirculation valve 9 and/or a leak in the intakemanifold.

The intake manifold pressure sensor measures the total pressure p-saugof the gas in the intake manifold.

Time-dependent traces of the intake manifold pressure are set forth inFIG. 2.

In the time span between t=0 and t0, the engine runs at idle. Here, anintake manifold pressure of approximately 300 mbar typically settles in.The engine is switched off at time point t0. According to the invention,the throttle flap is closed in a targeted manner. The rpm of theswitched-off engine then drops rapidly to zero. Because of the enginerotation still present when switched off, a dropping pressure couldstill be present for a short time in the intake manifold. In each case,a relatively slow pressure increase takes place up to the value of theambient pressure when no further mass flows flow into the intakemanifold except for the mass flow via the throttle flap. Here, the solidline in FIG. 2 is noted. In this case, the intake manifold pressurefirst sank below the idle pressure of approximately 300 mbar and thenincreased in a time span of more than 2 seconds to the ambient pressure(approximately 1000 mbar).

The broken line in FIG. 2 corresponds to a pressure trace as it is to beexpected for an open exhaust-gas recirculation valve. In this case, theintake manifold pressure increases considerably faster to the ambientpressure.

An embodiment of the method of the invention is shown in FIG. 3 whereinblock 20 identifies a higher order main program. Step 1 is reached fromthe higher-order main program 20 for controlling the engine functionswhen the engine is to be switched off. In this case, a targetedreduction of the air supply takes place via a reduction of the throttleflap opening angle in step 2. Step 3 functions for detecting the timepoints t1 and t2 at which the increasing intake manifold pressurereaches a first pressure threshold value P1 and a second pressurethreshold value P2. The difference dt of both time points, which isformed in step 4, is proportional to the rate of change of the intakemanifold pressure. In step 5, a comparison takes place of the differencedt with a pregiven threshold value. If dt is less than the thresholdvalue, this shows a mass flow to the intake manifold. This can beevaluated as an indication for the following: a defectively openexhaust-gas recirculation valve, a defectively open tank-venting valve,a throttle flap which is not closed sufficiently enough or for a leak inthe intake manifold (step 6). As a consequence, the fault lamp 12 can,for example, be switched on. If dt is not less than the threshold thenthis can be evaluated as an indication of the absence of leakage (OK)(step 7).

As a further embodiment, a system can be activated in a targeted mannerwhich supplies mass to the intake manifold. For example, an exhaust-gasrecirculation valve or a tank-venting valve can be opened in a targetedmanner so that a conclusion can be drawn as to the mass flow of thissystem from the comparison of the expected intake manifold pressuretrace with the measured intake manifold pressure trace.

1. In an internal combustion engine having an intake manifold to whichair is supplied and wherein an intake manifold pressure develops, amethod for detecting mass flows to the intake manifold of the internalcombustion engine including: means for controlling the air supplied tothe intake manifold; means for detecting the intake manifold pressure;and, means for evaluating the intake manifold pressure; the methodcomprising the steps of: when the internal combustion engine is switchedoff, reducing the supply of air to the intake manifold in apredetermined manner whereupon the intake manifold pressure changes asfunction of time; and, evaluating a trace of said intake manifoldpressure changes as a function of time to detect a mass flow into saidintake manifold.
 2. The method of claim 1, wherein said internalcombustion engine includes a throttle flap and the reduction of the airsupply takes place via a predetermined movement of the throttle flap ina closing direction thereof.
 3. The method of claim 2, wherein thethrottle flap is moved to a defined opening angle in targeted manner. 4.The method of claim 1, wherein, when the engine is switched off and fora closing movement of the throttle flap in a targeted manner, no furthersystem is activated which supplies the intake manifold.
 5. In aninternal combustion engine having an intake manifold to which air issupplied and wherein an intake manifold pressure develops, a method fordetecting mass flows to the intake manifold of the internal combustionengine including: means for controlling the air supplied to the intakemanifold; means for detecting the intake manifold pressure; and, meansfor evaluating the intake manifold pressure; the method comprises thesteps of: when the internal combustion engine is switched off, reducingthe supply of air to the intake manifold in a predetermined mannerwhereupon the intake manifold pressure changes as function of time;evaluating a trace of said intake manifold pressure changes as afunction of time to detect a mass flow into said intake manifold; and,wherein said internal combustion engine further includes a systemsupplying said intake manifold; and, when a rate of change of pressureexceeds a predetermined threshold value, drawing a conclusion as toleakage of the system.
 6. In an internal combustion engine having anintake manifold to which air is supplied and wherein an intake manifoldpressure develops, a method for detecting mass flows to the intakemanifold of the internal combustion engine including: means forcontrolling the air supplied to the intake manifold; means for detectingthe intake manifold pressure; and, means for evaluating the intakemanifold pressure; the method comprising the steps of: when the internalcombustion engine is switched off, reducing the supply of air to theintake manifold in a predetermined manner whereupon the intake manifoldpressure changes as function of time; evaluating a trace of said intakemanifold pressure changes as a function of time to detect a mass flowinto said intake manifold; and, wherein a system, which supplies a massflow to the intake manifold, is actuated in a predetermined manner and aconclusion is drawn as to the mass flow of this system from a comparisonof said trace with the measured intake manifold pressure.
 7. The methodof claim 6, wherein the system, which supplies a mass flow to the intakesystem, includes one of the following systems: an exhaust-gasrecirculation; a tank venting; and, a throttle flap at small throttleflap angles.
 8. In an internal combustion engine having an intakemanifold to which air is supplied and wherein an intake manifoldpressure develops, a control unit for carrying out a method fordetecting mass flows to the intake manifold of an internal combustionengine including: means for controlling air supplied to the intakemanifold; means for detecting the intake manifold pressure; and, meansfor evaluating the intake manifold pressure; the control unit comprisingmeans for performing the method steps of: when the internal combustionengine is switched off, reducing the supply of air to the intakemanifold in a predetermined manner whereupon the intake manifoldpressure changes as function of time; and, evaluating a trace of saidintake manifold pressure changes as a function of time to detect a massflow into said intake manifold.
 9. The control unit of claim 8, whereina conclusion is drawn as to a leakage in said intake manifold or in asystem connected thereto when said mass flow causes said trace to departfrom a predetermined shape thereof.
 10. The method of claim 1, wherein aconclusion is drawn as to a leakage in said intake manifold or in asystem connected thereto when said mass flow causes said trace to departfrom a predetermined shape thereof.